This invention relates to current detection in power conversion.
Power supplies include current limiting circuits for several reasons, among them, to protect internal components of the power supply from excessive power dissipation, to protect the source from overload, and to prevent damaging currents from entering a user's wiring and load.
In addition, zero current switching (ZCS) converters of the type described in U.S. Pat. No. 4,415,959, incorporated by reference, must limit their output current for proper operation since there is a value of load current above which zero-crossing will not occur. One such ZCS converter 10, shown in FIG. 1, has a leakage-inductance transformer 12 that transfers power from a primary 11 to a secondary winding 13. The power transfer occurs in a series of energy transfer cycles, where the switching frequency of switch 16 varies the amount of power delivered to the load 20.
Various control schemes may be implemented to keep I.sub.choke at or below a maximum value. For example, a resistive shunt 30 may be placed in the serial path which carries I.sub.choke, as shown in FIG. 3. The voltage across this resistor 30, V.sub.shunt, indicates I.sub.choke, and may be input to appropriate control circuitry to limit the value of I.sub.choke. In other schemes, the output current may be sensed magnetically (e.g., by means of a transformer with a suitable core reset circuit; by means of a Hall-effect device).